1. Field of the Invention
The present invention relates to a back-up power device and its application. More particularly, the present invention relates to a built-in back-up power device and its application.
2. Discussion of the Related Art
Computers have become so inexpensive that their use is widespread. Many computers are used, for example, in controlling production lines, calculation, and entertainment. A good back-up power source is thus becoming more important to prevent data loss in a power outage, interruption or glitch. The typical back-up power source is an uninterrupted power supply (UPS), which is designed to provide the computer with a stable power source to continue normal operations for a relatively long period of time after a power outage has occurred. For example, a work station is typically equipped with an UPS to allow uninterrupted operation. To provide such a stable power source over a relatively long period of time, a UPS is complex and expensive beyond the reach of the average user.
FIG. 1 is a block diagram showing a personal computer 11 equipped with conventional UPS 12. Internal power supply 13 of personal computer 11 includes electromagnetic interference (EMI) filter and power factor controller (PFC) 131, AC/DC converter 132, DC/DC converter 133, and feedback circuit 134. EMI filter and PFC 131 eliminate noise in the AC input power. The filtered AC input power is converted to high-voltage DC power by AC/DC converter 132. Then, the high-voltage DC power is converted to low-voltage DC power by DC/DC converter 133 to provide an operating voltage to personal computer 11, which includes, for example, a mainboard, a floppy disk drive, a hard disk drive (HDD), a compact disc read-only memory (CD-ROM) reader. Feedback circuit 134 adjusts the filtered AC input power in response to the high-voltage DC power output. Thus, since there is no power-storing unit in internal power supply 13, the low-voltage DC power output is interrupted immediately after the AC input power is interrupted. When such a power interruption occurs, personal computer 11 is improperly shut down. In computers running high-level operating system such as Windows 95/98, Windows NT, or UNIX, a power interruption can leave the operating system in an inconsistent state, leading to loss of data and time and labor expenses in restoring the operating system to a consistent state.
UPS 12 avoids data loss from a power interruption by providing stable AC input power. As shown in FIG. 1, UPS 12 includes EMI filter and PFC 121, AC/DC converter 122, DC/AC converter 123, charger 124, and battery 125. When the AC input power from the utility power source is operating, the filtered AC input power provides a converted AC power through the AC/DC converter 122 and DC/AC converter 123. The converted AC power is supplied to internal power supply 13 and is used to charge battery 125 through charger 124. When a power interruption occurs, battery 125 discharges to maintain a DC output to DC/AC converter 123 which, in turn, maintains the converted AC power. Hence, UPS 12 provides internal power supply 13 with stable AC input power during a power interruption for as long as battery 125 can continue to supply the DC output to DC/AC converter 123.
UPS 12 suffers, however, from some disadvantages. First, UPS 12 is complex and expensive. For home or simple office use, the cost of an expensive UPS outweighs its benefits of preventing data loss. Since only 3 to 5 minutes of uninterrupted power is required to shut down a computer properly during a power interruption, a simpler and less expensive back-up power unit which provides a personal computer power only for such a short period is desired.